The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A diesel combustion cycle produces particulates that are typically filtered from a diesel exhaust gas by a particulate filter (PF). The PF is disposed in an exhaust system of a corresponding diesel engine. The PF reduces emissions of particulate matter (soot) that is generated during a heterogeneous combustion process. Over time, the PF becomes full and trapped diesel particulates must be removed. During a regeneration process, the diesel particulates are burned within the PF.
An engine control system can estimate the particulate accumulation and determine when the filter needs regeneration. Once it is determined that the filter is full or filled to a predetermined level of particulate, the control system enables regeneration by modifying the combustion process and/or injecting fuel into the exhaust system. The fuel is injected into the exhaust stream after a main combustion event. The post-injected fuel is combusted over one or more catalysts of the PF. The heat released during combustion of the injected fuel on the catalysts increases the exhaust temperature, which burns the trapped soot particles in the PF. The elevated exhaust temperatures initiate oxidation of the stored soot within the PF. This approach can result in higher temperature excursions than desired, which can be detrimental to exhaust system components including the PF.
To minimize nitrogen oxide (NOx) emissions, portions of the PF may have selective catalyst reduction (SCR) elements. This type of PF is sometimes referred to as a 2-way diesel particulate filter (DPF)/SCR element. Although the 2-way DPF/SCR element reduces costs of an exhaust system, the performance of the SCR elements during regeneration is significantly reduced. A regeneration process can require 20-30 minutes of time to complete. During this period a majority of the PF is heated to temperatures of approximately 600-650° C. At these temperatures, the efficiency of the SCR elements to remove NOx is substantially reduced and thus the SCR elements are considered inactive.